Devices for dispensing plural component materials have become increasingly popular in recent years, as such materials have assumed more widespread usage in industry. As used herein, a catalyst (or first fluid) is mixed with a resin (or second fluid). While the terms catalyst and resin are used for purposes of convenience in reference, it is understood that other plural component systems may be utilized which might not normally utilize such terminology.
In dispensing and mixing such fluids, it is normally desired that they be dispensed in a fixed predetermined ratio which may be from all the way from 1:1 all the way up to 20:1. In more traditional systems, both fluids are metered simultaneously. Typically the flow on one side takes place at a relatively constant uncontrolled rate while the flow on the other side is varied to maintain the desired ratio. Also well known are mechanical systems, whereby two pumps are mechanically linked to produce a consistent mixture.
Also known are systems such as those sold under the PRECISION-MIX trademark by the assignee of the instant invention and generally described in European patent number 116879. In such systems, the two fluids to be dispensed both have a flow meter and a valve associated with them. A fixed amount of the first fluid is dispensed into a mixer and then a fixed amount of the second fluid is dispensed into the mixer, whereupon the process is repeated.
Such systems utilizing sequential metering work well but become less than accurate when used at higher flow rates. In particular, one of the downfalls of such systems results from the fact that the valves which are used to shut off flow do not have instantaneous response. Thus if the first fluid valve has dispensed fluid for 20 counts of the first fluid flowmeter and then ordered to close, several additional counts will probably flow through the valve before flow actually stops.
In the prior art devices, the only correction which takes place is that the counts representing the overrun are subtracted from the subsequent cycle of the same fluid. For example, if the first fluid normally dispenses 20 counts worth of material and the overrun amount to 2 counts, during the subsequent cycle, the two count overrun would subtracted from the normal amount and the valve would be ordered to dispense 18 counts.